Resource Conservation: Heat: Water Heaters

It maybe a simple process to heat water but it requires a certain amount
of energy. In this section, we look at ways to make sure that energy
does not go to waste. We have a special page devoted to
explain the heating technologies.

Overview:

Water Temperature: The
"cold" water that comes into your home (business) is a certain
temperature. We assume that it is about 50F. If you have
seasons, it will fluctuate but probably average out to 50F
throughout the year. The goals is to bring in that 50F water and
deliver it to different areas of your house (business) at a
temperature right for the job.

Hot Water Jobs: In a home,
the basic jobs requiring hot water are for sinks,
shower/bath, washing clothes and washing dishes. For businesses, it is about the same but sometimes your
state government may place certain requirements on those jobs.
We build most all our homes (and businesses) in such a way that
we can have our hot water do these jobs whenever we want
(on-demand).

Ways to heat the water: In general, there are 5 technologies
that can do all or part of our water heating job.

Conventional storage water heater: fills a tank of water
to a temperature to be used on demand.

Tankless (on demand) water heaters: Only heats water
as it is used.

Heat pump water heater: Uses Heat pump technology
to heat the water.

Solar water heaters: Uses the sun to heat all or a portion
of water heating needs.

Tankless coil water heater: Uses homes heating system to
heat the water.

How much do we want? Some people may say,
infinity. What they are really saying is, "I should never
run out of hot water if I am taking a one hour shower, while
doing dishes and filling the hot tub." A more pragmatic
person would want an amount that would fulfill peak usage
comfortably (enough for 3 showers and a couple of
shaves in one hour). In the next sections, we will challenge you to truly
figure out what your needs are.

How much energy do we waste heating water?
A lot. Yes, that is our answer! What we do know is your
situation will be different than the average, so we will
give you the tools to determine what it right for you. On
average 20% of a households energy bill is used to heat
water. Many hot
water heaters are on 24 hours a day. This way they are
always ready to heat new water or to heat the already heated
water that became cooler.
The waste is heating water that has already been heated and
the efficiency by which it heats.

Energy Types: In general you can choose to use
electricity, gas and the sun (solar) to heat water. However, some
people use geothermal, wood stove, coal, diesel and many
other raw energy types to provide heat to water.

How much money can I save (ROI)? This is
a great question but complicated to answer. Hopefully, we
give you enough information to answer that question
throughout this section. We do this though links and
references, and through calculators that can help for many
peoples (and businesses) situations. One thing that will be
common for all technologies discussed is that conserving hot
water will go a long way to conserving energy (and money).

Conservation First:

Please, forgive us for breaking our usual standard write up but
we feel that a little has to be said about how hot water is
used. In order to
calculate what your hot water needs are, we feel that an evaluation of
the things that use hot water should be the first thing to do.
You may skip this part if you have done this already.
The question is, are your sinks, showers, washing
machines and dish washers operating with the right amount of hot
water? Do they need more? Can they perform with less? In other
areas of Greencompletely.com we talk about water conservation
and some of that is conservation of hot water. We suggest you
check those sections out.

Why? It does the most good. Conserving the water you heat saves
more energy than trying to save energy making the hot water. If you calculate your needs for water
heating without optimizing the devices that use hot water, you
may buy a bigger system than you need.
It is simple, make your conservation changes first. Then,
make your water heating optimization last. This could have a
much faster return on investment.
This includes, but is not limited to, evaluation of your
shower heads, your sink aerators, your dishwasher type, your
washing machine uses and types.

Energy Efficient?

Fuel Efficient: As stated in the
"General Comments" there are many choices of fuels to heat our
water. In general the choices are electricity, gas and solar. Of
course, there are other choices but we will not cover them a lot
here. Solar: The main type of solar heater is one that gets
heat from the sun (not electricity).
This is considered the "free" fuel option. There are two general types of heaters: "active" and "passive".
There are two types of active:
"direct circulation" and "indirect circulation" systems.
There are also two types of passive systems: "integral
collector" and "thermosyphon". Active
systems tend to cost a little more but are more efficient then
passive systems. Regardless
of where you live, you will probably want to have a back up fuel
source when the sun is not out. Gas: When we say "gas" in this section we mean
Natural gas and Propane gas. Gas water heaters are rated among
the cheapest ways to heat water. It is fast, cheap and
reasonably efficient. Many of the tankless options only work with gas.
However, if gas is not feasible at your location or you have a
problem burning a hydrocarbon, gas may not be for you.Electricity: A very common way to heat water.
This fuel source may not be as cost effective (long term) as
solar or gas, but electricity is usually always available.

Money Efficiency: Picking a water heating system to
replace an existing system or on a new building can be difficult.
It will depend on initial costs, maintenance costs, fuel costs,
consumption and a few other factors. One thing we
would like to point out, technology in this area is changing,
therefore, cost feasibility may not be the same as a few years
ago.
We will give you the tools to determine that
for yourself during this write up.

Energy Efficiency: There are 5 water heating methods mentioned in the
"General Comments" section. They are:
Conventional storage, Tankless (on-demand), Heat Pump, Solar and Tankless coil.
The reasons to use these technologies is as varied as there are households and
businesses out there.
We will try to simplify your choices. Weather Dependence: Some systems will work better
if it is cold out and some will work better if it is warm out (does not freeze
very often). Conventional storage and tankless demand-type will
generally work well in all weather (indoors). However, for cooler climates Tankless Coil and a few types of Solar could work
well. For warmer (sunnier) climates, Solar and Heat Pump may be
a better choice. Usage Dependence:
Hot water usage can play a big part in choosing a technology.
Big families and big businesses can demand a lot from their hot
water system. Helper technologies:
We do want to make a distinction here. Some of these technologies
can be made to help other water heating technologies. Therefore, they
can either heat your water or help heat your water.

1 Calorie = Amount of energy required to raise the temperature
of 1 gram of water 1deg C.

We can show you a fancy derivation but for now we will just say that we put
this fact into a spreadsheet and came up with the following numbers.

We get:
2111 Calories to raise 1 gallon of water 1 deg F.

That does not do us any good until we know it in electrical power or
gas use (KWHR or Therm).

0.00245 KWHR to heat 1 gallon of water 1 deg F.
Or
0.0000837 Therm to heat 1 gallon of water 1 deg F.

Special Note:
Gas companies will charge based on different ways to measure the
gas. One common way is CCF and it is almost the same as Therm
(about 3% different).

Now if the water is 50 deg F and we want to bring it up to 120
deg F. The raw amount of power needed to heat a gallon of water
is:

0.172 KWHR to heat 1 gallon of water 70 deg F
Or
0.0059 Therm to heat 1 gallon of water 70 deg F

This is the raw amounts of energy required. The EF of the
water heater will tell you basically how much energy you will
expend for that gallon of water.

Assuming you are comparing two water heaters that both have
an EF of 0.7 and one is gas and one is electric. Energy spent
to heat 1 gallon of water 70 deg F is:

0.245 KWHR
And
0.0084 Therm

In the "Green Calculators" section we will help you calculate
the costs of heating your water.

Other Considerations (Please Read):

The majority of people do not like to change things in their homes. If the
home is newly built, the contractor will usually pick a water
heater and install. When water heater breaks, most of us, replace it with
the same type and size water heater. Doing this we do not get in trouble.
We let the contractor worry about the prevailing codes and since the
heater was working for us before, why not replace it with the same thing.
That is the easy thing to do.
However, since you are reading this, we assume you want
to find what is right for you and your needs. When doing this research, you should be
aware of factors besides cost and efficiency.

Codes: Generally, this is the reason most people do not
change out their water heater. A professional contractor (plumber)
have the skills and knowledge of all the requirements.
If you contaminate the water supply, it can be a big problem.
If you are a
do-it-yourselfer, you need to understand the local codes well to undertake
any project like this. Neighborhood covenants may also need to be consulted.

Conservation First: We said this before and we will say
this again. Make sure you have installed your water conserving devices
(shower heads, aerators, etc.) before you change out your water heater.

Know Your Energy Rates: All too often people
"sell" things because you will "save" tons of money by saving
energy. It usually is not a lie that you will save energy,
however, what you need to do is determine cost of ownership and
any inconvenience that you are not willing to deal with. Do not
be "sold", you should buy with confidence. 1/2 hour of
research (perhaps on our site) can make a big difference.

Safety:
Of course, safety should always be a concern when doing any project. Beside
the basic safety concerns during installation/removal of
water heating systems, you should be concerned about long
term safety. You should ask if this system will hurt your roof (solar collector)? Will the water get
too hot and scald my children? If there is a leak, do you have a
system in place to take care of it? Will the water be
potable (generally drinkable)?

R-Value: The "R-value" of a tank used in
the storage of heating water Usually will range from about 5
to 25 and it is usually a measure of insulation a heater
has between the tank and the environment outside the tank.
In general, for every inch (thickness) of the insulation
your R value increases by about 8.3. Therefore, a tank at R
16 would have about 2 inches of insulation. What amount is
right? In general, you can not go wrong at about an R-value of
15 or better with conventional tank water heater.

Efficiency Gadgets: People have come up with
many things to help make your water heating system more
efficient. Some of these things are: insulating blankets,
heat traps, pipe insulation and more. These items can save
big but under certain conditions. If you are not heating
your water in those conditions you may only save a few
pennies a month. We
address some of these items later.

Warranties: As with most
things, the longer the warranty the better the quality. With water
heaters this usually means better quality parts, technologies
that keep it from breaking and maybe a higher R-Value. Some elements
may have coatings or be made out of different materials, tank liners
could be better and there could be more energy saving features.
Usually the longer warranty heaters will be a better value
long term.

Installation:

Do It Yourselfers, Beware: Hot water heaters, as you
probably are discovering can be complicated no matter the technology you
choose.
There is nothing preventing you from installing
yourself, but in most areas, if you do not do it right, it can
be a big problem.
Make sure you know exactly what is required in
your area to install whatever you choose.
If you are looking for rebates on some of the
technologies, you may be required to buy systems with the
EnergyStar rating and installed by a professional contractor (or
solar contractor). These tax credits and rebates may be worth
more than the cost of the contractor and the EnergyStar label.
We did a quick YouTube search and found some
do-it-yourself videos (we did not make any of these) that
may help you. However if you install yourself it is your
responsibility.

Requirements For Installation: If you buy a
system, then later you find out that you have to spend $1,000's
tearing up your house to install a new system, it may not be
worth it. Know what you are getting into.

Non-Do-it-yourselfers: Do not wait till the
heater is broken before you start to make decisions about water
heating. When your water heater breaks, all you want is to have
running hot water again. The last thing you need to do is let a
contractor make the decision for you without knowing the long
term costs.
In general, most
contractors are knowledgeable and really want to help. They will
ask questions about water use habits that will help him/her make
recommendations. However, knowing what you want ahead of time
could save a lot of time and money in the long term.
Use the information here (or elsewhere) to pick a
heating technology. Check out contractors with the BBB or
Angie's List.
When you have the technology picked and the contractor, you can
pick sizes and features so that when the time comes, you will
make decisions that are right for you.
Most contractors can install conventional tank,
tankless and heat pump type technologies. However, usually you
will need to go to a solar contractor to install solar
technology.

Disposal:

Disposal is something that we may have to worry about, when
replacing our water heaters. If you have a contractor replacing
the heater, they might just take it away when they are installing
the new one. Well,
what does "away" mean?Conventional Tank Water Heater: Many
contractors will have a recycling procedure. If you need to
dispose of a conventional tank water heater many cities and
utility companies have buy back programs. However, many systems
contain a lot of recyclable metal. You may be able to take the metal to a scrap
yard. The insulation and some of the plastic parts will not be recyclable.
Tankless Water Heater: These units are brief case sized.
That means that they can potentially contribute less to the land fill. They
would also contain a lot of recyclable metal. However, it is not the
disposal of a unit but the installation that could be a problem. You may
need to string new wire, upgrade your utility box. You may even have to
pull out entire sections of sheet rock to install one of these units.
Every house (business) will be different but it may generate extra garbage.

Solar Water Heater: It seems like a solar system
is a conventional tank water heater with some extra stuff to collect
solar energy. In most cases, that means you have 3 to 5 times more disposal
at the end of life of the system. We also looked all over the
SRCC site
and could not find any requirements for these parts to be recyclable.
Most of the do-it-yourself sites construct units that are
mostly non recyclable (PVC pipe, glues, paints, tanks, etc).
Even if these systems were completely recyclable you still
have a larger disposal problem. For the active systems that
require a "non freezing liquid" for their heat exchanger,
this would probably be a much bigger disposal problem. Heat Pump Water Heater: Most all of these systems
we have seen are a conventional tank water heater with extra
equipment
built on top. So, it is an extra compressor, tubing and some other stuff.
Many have Refrigerant 410a as the heat exchange liquid and that tube is
immersed directly into the tank of water. So, you have an extra compressor,
extra wiring, extra tubing and a refrigerant to deal with.

"Standby" Power Loss:

Everyone talks about it.
"Standby power loss". This is the power your conventional
tank water heater uses to reheat water that it has
already heated but has fallen below the set temperature.
This forms the impetus for creating tankless water heaters
and heating systems.
But how much is it for
typical water heaters? We have looked everywhere for the
answer. No one is providing a clear answer. Some sites say
20-30% of your water heating bill, and some place it at a
few %. They state average numbers from national averages but
we have not found a concrete data set to help you
individually.

What We Know: As long as the water temperature
in the tank is higher than the temperature of the room,
there will always be heat loss.
The bigger the tank capacity the faster the heat loss.
The higher the temperature is set the faster the heat loss.
The lower the temperature in the room the faster
the heat loss. The higher the R-Value, the slower the
heat loss. If your water heater is always on, your heating
elements will come on and off within a range of temperatures
around your set point.
We help you figure this out in our "Green Savings
Calculator" section below.

Recovery Rate:

If you have a storage tank water heater when hot water
leaves the tank
new cold water enters. The heating elements turn on
automatically to start
heating that new water. How quickly can the new water come up
to the desired temperature?
It depends. There are a few factors that you will need
to use to calculate it yourself.
This "recovery" rate is calculated in Gallons per hour.
However, what we have discovered is that if you have a
tank all one temperature, You can remove quickly about 70%
of the water at the set temperature. The rest will be a
mixture of the new cold water and the remaining hot water.
On a 50 gallon tank that is the first 35 gallons.

As a tank is recovering from loosing hot water our research
basically says to also use that 70% factor for heating up
the new cold water.
To make the calculation of Recovery Rate we need to use
a few factors. First we use the wattage of the heating
element (or BTU/hr if gas). We next use the cold water
temperature, the set temperature of the tank and the
efficiency factor (EF) of the tank (about 0.93 for electric
and about 0.65 for gas). Lastly we apply the 0.7 factor
(recovery factor).
We put a calculator for this in the "Green
Savings
Calculator" section below.

Of course, there is no recovery rate for tankless
because they make hot water when it is demanded.

Tank Size:

Conventional Wisdom "Buy to Peak":
In just about everything we read while researching this area, everyone
says
"buy to peak".
For conventional storage tank systems you figure out
what is the possible use for any one hour in your
home. Then you buy something rated with a "first hour" performance
near that number.
For a typical house of 4 that might be 2 showers, 10 minutes
at the sink and a load in the dishwasher. That would be 40 +
5 + 7 = 52 gallons of hot water. Most people would then buy
a 50 gallon water heater (56 gallon first hour rating)
For tankless heaters it is a little different. The
question becomes how many devices are possible to be on at
the same time. Let us say that someone is taking a shower, someone washing
their hands, and the dishwasher is running. That could be 2 + 0.5 + 1.5
= 4 gallons a minute required by the tankless water heater.
So you buy a 4-5 gallon a minute system.
If you go to other web sites and to home improvement
stores you will see other guides. One guide that is popular
is based on the number of people in the house. Another guide
is based on the number of bathrooms.

However, for household that have implemented recent conservation
strategies (low flow showerheads, HE washer, etc) these old
guidelines may deserve rethinking. If you install water conserving devices and apply the
same logic, a family of 4 may only need a 30 gallon water
heater or a 2
gallon a minute tankless heater. These options would cost
less for their type of water heating short and long term.

Our experience shows that the actual flow for some
devices can vary from the rated value. We suggest you
measure your flow rates especially for sinks and showers. If
a shower head is rated at 2.5 gallons a minute at 80 psi your
flow may be as low as 1.2 gallons a minute (at say 30 psi).
A shower is a mix of hot and cold water, so if you use 20
gallons of water for your shower only about 14 gallons are
hot water. Similarly, faucets and clothes washing typically
do not use 100% hot water.

An awareness of how much water your piping may hold can
help you calculate some of your water heating jobs. We
created a table below to help you with that.

Greencompletely.com Wisdom: "Buy to Likely":
Instead of counting up what is
"possible" use in a 1 or 2 hour peak at your home you start by choosing
the lowest capacity water heater (say 10 gallons).
Next you look at its recovery rate (say 3 gallons an hour).
At this point you make a list of uses possible in a
day.

Pretend that list looks like
this:

Shower: 7-12 gallon hot per shower, 4 showers

Clothes wash: 5 gallons hot (warm cycle), 1 loads in a day.

Dishwasher: 6 gallons hot, 1 time a day.

Sink use: 10 gallons hot, 30 minutes of use spread through the day.

This is about 60 gallons
of use throughout the day.
Then you ask the question,
"Can we find a way to have
a 10 gallon hot water
heater with a 3 gallon an
hour recovery, and never
run out of water?" If your
answer is no, that is
fine.
Pick the next water heater up. Say that is a 15 gallon
water heater with a 5
gallon an hour recovery.
Ask the same question. If
the answer is still "no".
Select the next one up
(say a 20 gallon with 7
gallon an hour recovery).
Seriously think about how you can use it and convenient
wait times between showers
and washing the dishes.
These wait times may only
need to be 10-20 minutes.
A 20 gallon hot water
heater may make 30 to 35
gallons of hot water
available in a 2 hour span
of time. A small bath may
be possible with a 20
gallon tank.
When you get to the 30 gallon tank
usually that is a 220V
appliance. It will have
faster recovery and you
have quality choices that
you do not have with the
110V 20 gallon and below.
Higher R-value, circulation
and a
brass drain are just a few
possible upgrades. A comfortable
bath is very possible with
a 30 gallon unit.

For fun we calculated, in a spread sheet, how many feet
a gallon of water would take up for different pipe (inner) diameters.

Pipe Diameter
(inch)

Approx. Feet Containing 1 Gallon
(feet)

3/8

175

1/2

100

5/8

65

3/4*

45

* Typical Home

Temperature Setting:

In this industry, there seems to be 3 magic numbers: 120 deg F, 130 deg
F and 140 deg F.
120 deg F is usually the factory default temperature setting. Therefore, when
a contractor installs the system it will be set at 120 deg F.
130 deg F is basically a goal temperature of water to
get dishes clean and to kill bacteria. Clothes washed near
this temperature will get most all the bacteria and grease
out of the clothing just from the water temperature.
140 deg F is usually the maximum setting of the hot water heater.
Some heaters will actually add cold water if it detects water above 140
deg F.
Over all, the lower the temperature setting the less
energy you will use to heat your water. However, there are
some jobs you ask of hot water that you will want to think
about the temperature a little more.

What temperature is right?
Many modern dishwashers have built in heating elements. If the
dishwasher "sees" a temperature below the goal temperature (probably
130 deg F) it will turn on the heating element. However, some
only have the capability to warm the water only about 10 deg F.
For clothes washing machines, the "hot" wash is
whatever temperature it gets from the hot line. If there is
a great distance between the hot water heater and the
washing machine the final temperature of the "hot" cycle
could be 10 deg cooler than the setting of the hot water
heater.
We suggest a setting of 125 to 130 deg F if you have an
older dishwasher. A setting of 115 to 120 deg F should do
well with modern appliances.

Expecting Company? Make your hot water heater bigger.
If your hot water heater is set to 120 deg F and you are worried
that your hot water heater will not keep up with the demands of having
visitors (showers especially) we suggest you increase the size of your
water heater. You can do this by raising the temperature of the water
heater from 120 deg F to 135 deg F, then simply lower it when the company leaves.
This will give approximately 20% more initial capacity for showering
(it won't speed recovery rate).

What We Have Forgotten:

Of course, we can not write about what we have forgotten.
However, in our research we have omitted some details. This
area is so vast that we would need to make our write up about water heaters
twice the size. We do give more details about the
water heating technologies
in a separate write up.

What we strived to do is to give you enough information so that you
can make an informed decision about buying your next water
heater. For those that want additional info,
we have provided references below. The decision you make can
last 8 to 15 years, so it may be worth spending some time to
make the best decision.

Our Picks:

We just have two things to say.
"Less Is More"
and "Keep It Simple"

Less is more: Less hot water use is much
more energy efficient than trying to do something fancy.
When buying a water heater we say, the smaller the better.
You can not get around how much energy is required to make
hot water hot. However, having a smaller volume of water to heat reduces
the standby power losses your heater will have. Also, we have
found some water heaters (with plastic tanks) that reduce heat
loss by a factor of 2 to 4.

Keep It Simple: We can not stop you from
changing the fuel source or water heating technology in your
house. However, the simplest thing to do is to keep it the same.
Any of the changes can cost you $1,000's. You may have to rip
down sheet rock and do other invasive things to your house. All
the while, you may contribute to the landfill much more than you
want in the long term. We encourage you to seriously consider
the total cost of changing your system.

If your are getting a tank (conventional tank or heat pump) you
may want to locate your water heater on the south side of your
house in front of a south facing window. If you open the blinds
during the day (in summer) you will increase the temperature of
that room making a heat pump more efficient and reduce "standby
power loss" for a conventional tank. This should also increase
the water temperature of the cold water by a little bit. In the
winter, you may want to insolate the window.

Having said all of that, we are having a hard time
finding quality products in this area.
We have put a few choices in the store but this does not serve
every household or business.
Our pick from Rheem, is the Marathon series of water heaters.
The smaller water heaters are for households between 1 and 3
people (see our sizing calculator below). These water heaters are what
is called "Point of Use" heaters and are usually not for heating
the water for a whole house. Therefore, heater producers do not
have to give you as much information about point of use as they
do about the "home sized" water heaters. We have yet to find a
quality gas powered 20 gallon heater.
The Marathon tank (from Rheem) is polybutene which we believe is not recyclable
but very durable and can hold heat longer. If you do not take baths or take
low water baths the 20 gallon tank should do all your heating jobs.
Go to the store to see them.

Quick Note On Savings:

As we have said before, conservation first. The way
to save the most money, energy and water is to not
use the water in the first place. Install water conserving
shower heads, aerators on the sinks, HE clothes washer, etc.
Doing all of that first,
will help you determine the size of the water heating system you actually need.
When you go to buy a water heater, tell them what you need not the other
way around.

See if you can be "water aware" when using hot water. See
if you can time different events (dishwashing, showers, etc.) so that
you will not run out of water. Once you begin doing that it will get
easier and eventually you won't have to think about it.
The alternative is to spend more money on standby power
loss, and bigger costly systems. This can waste $100's of
dollars a year.

Green Savings Calculator:

Calculators For Hot Water Heating:

Useful information for calculators:

This is a basic map of water temperatures across the nation.
Click on it to see an average in your area (EPA Site).

To determine back to back showers possible with a small wait time,
enter the information below (use winter inlet temperature typically
5 to 15 deg F cooler than your average).
We suggest you measure your shower head
flow rate before you make this calculation. We assume shower is 100 deg F and no other hot water use during
this period.

ELECTRICITY:

Water Inlet Temp (F)

Hot Temp Setting (F)

Recovery Efficiency

Heating Element (Watts)

Showerhead Flow Rate (gal/min)

Time for each Shower (min)

Wait time between showers (min)

Tank Capacity (gallons)

Results:

Recovery Rate hotgal/hour

Showers*

* Negative numbers mean infinite showers

GAS:
For those with gas water heaters, use 6900 Watts in the "Heating Element"
box to estimate for a 30,000 BTU/HR gas burner. 9200 Watts for 40,000 BTU/HR. 11500 Watts for 50,000 BTU/HR.

When figuring out the water heater size, consider all the changes that
have happened and may happen in your household. If you have changed
out showerheads and faucet aerators, then chances are you may not need
as big of a water heater. Please, measure your
devices before you make these calculations.
Conventional wisdom is to look at your peak 1 to 2 hours of hot water usage during a day.
Consider how many showers, loads of
wash, loads of dishes, and total sink use during that peak time.
In addition, we ask that you look at what is realistic
and common usage (not the usage you might see once a year).
Then, we ask you to consider some wait times between those events.
You will be surprised just how big an effect a few minutes can have. To calculate the peak tank size, we assume
water heating in the winter months.

For this calculation
we assume shower use first.
We assume faucet use throughout
the two hours. Then, if the washing machine and/or dishwasher are
used you will wait a small amount of time after showers to use them.
You may also set a wait time after the dishwasher to start the clothes
washer. If you set the wait times to 0, that will mean you
start the dishwasher immediately after the last shower and start
the clothes washer at the same time as the dishwasher. By changing
wait times and other entries you can see the effect on your
"best fit" water heater.
Here we assume: Showers are 100 deg F, Sink use is 60% hot water, Dishwasher is
100% hot water, Warm cycle on Clothes washer is 40% hot water, Hot cycle on clothes
washer is 100% hot water. This calculator ignores leaks and pipe heat loss.

Standby Energy: This is energy used, usually by
conventional storage tank systems, to reheat water that has already
been heated.

Dip Tube: The tube leading into the bottom of a
conventional water tank from the cold water supply.

Recovery Rate: The rate at which a water heater
can generate new hot water when it senses new cold water in the tank.
It is based on the wattage of the element (electric) or the btu/hour
of the burner (gas).
The recovery rate is express in gallons/hour. Usually the printed
recovery rate is to raise the temperature 90 deg F.

Thermostat: a device that activates or
deactivates the heating system based on the temperature it
measures and the temperature that is "set".

LCD: Liquid crystal display. Made of Indium Tin
Oxide. Used as a display monitor for thermostats.

Return on Investment (ROI):
Usually measured in an amount of time to
pay back an investment by saving money that you would otherwise
spend.

Energy Factor (EF): This is basically a measure
of the efficiency of the water heating system. It is the amount of energy required to
heat the water used divided by the actual energy used by the heater.
The general range for gas is about 0.5 to 0.8 and electric is between 0.75 to 0.95.
This includes "standby energy" loss.

Solar Fraction (SF): The the fraction of heating a solar
heating system can do compared to no solar heating. 0 being none and 1 meaning all
the water you use is heated by solar. Typical solar fractions run between
0.5 and 0.75.